Hello, stomach pain and black stool raise concerns for gastrointestinal bleeding, so visiting a doctor is recommended. Note though that some drugs for the stomach and the intestines contain substances that stain the stool. You can have a look at the drug s summary of product characteristics (which should be inside the box). Breathing difficulty with the antihistamine, which I suppose is the allergy pill, is not expected. The cold may do so though. Breathing difficulty can be expressed and interpreted in many ways by patients, so I can t comment on that without clinical examination. If you do feel shortness of breath (like if the oxygen in the air is not enough) then you should visit the ER immediately. There is no charge for this answer, so don t worry! If you d like you can send more details about your problem for a more detailed answer. Please include the names of the drugs you ve used and a description of the cold , that is its symptoms in detail (like if you had fever, cough, runny nose, etc). I hope it helps! Kind Regards!